This invention relates in general to apparatus and methods for working on sheet material and deals more particularly with improvements in apparatus and methods for performing a repetitive size-dependent work operation on woven fabric wound on and fed from a supply roll.
The fabrics with which the present invention is concerned, and which include wool, cotton and synthetic materials, comprise fibers which have a developed surface texture characterized by fuzzy surface projections, or the like, which tend to adhere or interlock with projections on adjacent fibers or threads in the fabric or web. Such characteristics are generally desirable in a fabric and prevent the threads which comprise the fabric from becoming displaced relative to each other within the fabric web structure, thereby maintaining the integrity of the structure.
In the manufacture of articles from such fabric, it is customary for the fabric to be made-up into rolls or bolts to facilitate convenient handling and storage. However, the process of winding fabric to form a roll or bolt inevitably subjects the fabric to stretching forces resulting in tensional, compressional, bending, shearing, and twisting stresses within the bodies of the threads which comprise the fabric. Further, adjacent surface projections on each thread or fiber tend to interlock or become entangled with each other and with the surface projections on adjacent threads or fibers and resist the release of stresses within the wound fabric when the fabric is payed-off the roll or bolt. More specifically, adjacent entangled surface projections on the curved inner side of each fiber of the wound fabric, which are compressed relative to each other when the fabric is wound, resist separation in tension as the cloth is payed-off the supply roll, whereas adjacent entangled surface projections on the curved outer side of the fibers, which are subjected to tension when the fabric is wound, are forced toward each other and also resist separation as the fabric is straightened and tangentially payed-off the supply roll S. The residual internal stresses within the fibers and the additional stresses produced by the interlocking surface projections resist relaxation or shrinkage of the spread fabric. Creep is a function of time, therefore, when the stresses responsible for this phenomenon are relieved, as by unrolling or spreading the fabric, the fabric will relax and undergo slow return to its normalized or unstressed dimensions.
An accepted procedure for stress relieving wound fabric is to unwind the fabric, spread the material upon a supporting surface and allow sufficient time for it to relax or shrink to its proper size. Only then can cutting, printing or other size-dependent operations be performed on the material. However, this waiting period may result in costly machine downtime. Further, the provision of special table facilitaties to accommodate the fabric during the waiting period, while it is allowed to relax, adds further to the cost of the fabric processing operation in the form of additional equipment and increased floor space requirements. The present invention is concerned with the aforesaid problems.